The manga makes both of the main characters make more sense with fewer words/scenes, surprisingly.

One thing that really bothers me is how one of the main characters was rewritten to be more so much more shallow-ly characterized than he was in the manga. Please keep in mind that the manga is maybe 60 pages total - how do you manage to reduce a character's depth when you turn 60pp of mostly pictures to 2h of content?? He went from a realistic, if eccentric, person to a weird caricature of "innocent and imaginative". Disappointing.

The other main got a sort of similar flattening-out, but not to such a jarring degree.

Beyond that it was fine. Acting in the more bastardized character was kinda wobbly, but he wasn't given great material.

I can't tell you more without spoiling things, so I'll leave it up to you to hunt a full plot outline elsewhere (Wikipedia or forums are a great source of spoilers)! Either way, I definitely recommend finding the manga and reading that instead.